Cesarean section is the most common obstetric surgery worldwide. Epidural anesthesia has become the preferred anesthesia method for cesarean sections due to its definite analgesic effect and minimal impact on mother and baby. To ensure postoperative analgesia, intrathecal administration of morphine (the preferred opioid for obstetric intrathecal analgesia) is a routine clinical protocol, but morphine-induced postoperative pruritus is a common adverse reaction. A study targeting the cesarean section population confirmed that the incidence of pruritus after epidural morphine administration is as high as 40%-75%.Transcranial direct current stimulation (tDCS) can enhance the activity of GABAergic inhibitory interneurons in the spinal dorsal horn through the cortical-spinal descending pathway, reverse the inhibitory effect of morphine on them, and restore negative feedback regulation of itch-specific GRPR⁺ neurons; at the same time, it downregulates the phosphorylation level and membrane expression of μ-opioid receptors in the spinal dorsal horn, weakening the receptor activation efficiency of morphine. On the other hand, tDCS can reduce peripheral nerve excitability, decrease mast cell degranulation in the skin, and reduce the release of histamine and tryptase; simultaneously, it inhibits the activation of glial cells in the spinal cord/cortex, decreases the secretion of pro-inflammatory factors such as TNF-α and IL-6, and blocks the vicious cycle of 'inflammation-receptor upregulation-itch exacerbation,' thereby reducing the occurrence of itch.This study aims to explore the effect of transcranial direct current stimulation (tDCS) on the incidence of morphine-induced itching after cesarean section by inhibiting the central itch perception circuits in cesarean section patients and antagonizing the disinhibitory effects mediated by μ-opioid receptors in the spinal dorsal horn.

Inclusion Criteria:

• Age 18-40 years, gestational age 37-41 weeks, singleton full-term pregnancy;
• Planned elective or emergency cesarean section, using epidural anesthesia (0.1~0.2 mg/kg of morphine administered intrathecally during surgery);
• American Society of Anesthesiologists (ASA) classification I-III;
• Conscious and able to cooperate to complete scale assessments, serum sample collection, and postoperative follow-up;
• Voluntarily participate in the study and sign the informed consent form.

Exclusion Criteria:

• Presence of contraindications for tDCS (such as skull defects, intracranial metal implants, history of epilepsy, coagulation disorders);
• Allergy to opioids or a history of severe OEI;
• Presence of skin diseases (such as eczema, urticaria), liver diseases (cholestasis), mental disorders, or cognitive impairments;
• Coexisting pregnancy complications (preeclampsia, gestational diabetes, autoimmune diseases);
• Use of medications within the past week that may affect itch assessment, such as antihistamines, 5-HT3 receptor antagonists, or anti-inflammatory drugs.